1. Field of the Invention
The present invention relates to an image reading apparatus including a transmission type projection screen for reading an image projected on an inner surface side of the screen from an outer surface side thereof, a projection optical system for projecting an image onto the inner surface side of the projection screen, and a reading sensor moved across a projection optical path and in a sub-scanning direction orthogonal to a main scanning direction, for reading the projected image in an image reading mode.
2. Related Background Art
Typical examples of the above-mentioned image reading apparatus include a microfilm reader or a microfilm reader printer which has an image reading function.
This comprises a transmission type projection screen, a projection optical system for enlarging and projecting the image of a microfilm onto an inner surface of the projection screen, and a reading sensor moved across a projection optical path and in a sub-scanning direction orthogonal to a main scanning direction for reading projected image information in an image reading mode.
In a reader mode, the reading sensor is moved to a retreat position outside the projection optical path of the projection optical system and is held in the stop and standby state such that the image of the microfilm, which is enlarged and projected onto the inner surface of the projection screen, can be read from the outer surface side of the projection screen.
In the image reading mode, the reading sensor is moved and driven in the sub-scanning direction across the projection optical path from the retreat position outside the projection optical path of the projection optical system. Consequently, the projected image information of the microfilm on the projection screen is photoelectrically read.
The image information thus photoelectrically read is transferred to a printer section, and is then output as a hard copy through an image forming operation, or is recorded and stored in a memory section.
In such an image reading apparatus, the projection screen is of a transmission type. Therefore, in the image reading mode, unnecessary ambient light that transmissively enters into the inside of the projection screen from the outside thereof is entered into the reading sensor while overlapping with a normal projected image information light, resulting in deterioration in the quality of the read image or copied image in some case.
As described in Japanese Patent Application Laid-Open No. 3-231736, a light shielding member (shutter) of a double door type is provided on each of the right and left at the inside of the projection screen and is closed in an image reading mode to wholly cover the inner surface of the projection screen, thereby shielding an ambient light which is entered into the inside of the projection screen from the outside thereof.
Moreover, there has also been known a method in which a slit and a mirror are provided so that an ambient light is not entered into the reading sensor in the image reading mode.
However, in the case in which the light shielding member of a double door type is provided as described above, it is necessary to wholly cover the projection screen. Therefore, as the projection screen has a larger size, the cost of the light shielding member or the like is increased. Accordingly, components of the apparatus cannot be provided in a portion where the light shielding member is opened or closed like a double door. Furthermore, since the whole inner surface of the projection screen is covered with the light shielding member during image reading, a displayed image plane cannot be seen.
By the arrangement of the slit and the mirror, the size of the apparatus is increased even if the ambient light is not entered into the reading sensor in the image reading mode, and furthermore, the ambient light cannot be shielded completely.
An object of the present invention is to provide an image reading apparatus capable of reliably blocking the incidence of unnecessary ambient light on a reading sensor in an image reading mode, thereby enhancing the quality of a read image or a copied image and allowing one to see a displayed image plane on a projection screen also in an image reading mode without increasing the size and cost of the image reading apparatus and changing the arrangement of a mirror of a projection optical system in a conventional apparatus.
In consideration of the above-mentioned circumstances, the present invention provides an image reading apparatus comprising a transmission type projection screen capable of reading an image projected on an inner surface side from an outer surface side, a projection optical system for projecting an image onto the inner surface side of the projection screen, reading means moved in a projection optical path between the projection screen and the projection optical system for reading the image information in an image reading mode, and light shielding means capable of being moved corresponding to a position where an ambient light incident from the outer surface side of the projection screen, reflected by the projection optical system and entered into the reading means, is blocked in the image reading mode.
According to the present invention, it is possible to properly shield the ambient light entered into the reading means in the image reading mode and to eliminate the bad influence by the incidence of the ambient light, thereby enhancing the quality of the read image.